This invention relates to a pressure relief valve and, more particularly, to a pressure relief valve in which an additional loading force is applied to its valve member.
Pressure responsive relief valves are used in many applications to prevent operating systems utilizing pressurized fluid from reaching dangerously high pressures. Such valves usually include a nozzle having a valve seat which is normally closed by a valve member slidably disposed in the body of the valve. The valve member typically is biased to a closed position against the valve seat by a compression spring, or the like. When the system pressure exceeds a predetermined set value, the valve member opens and places the nozzle passage in fluid communication with an exhaust port in the valve body. When the pressure in the nozzle passage then decreases by a specified incremental amount to arrive at the reseating pressure for the valve, the valve member is again forced into a seated position on the valve seat under the action of the compression spring to close the valve.
In these types of arrangements, the valve member must seat very tightly on the valve seat to prevent leakage, particularly at pressures approaching the set pressure of the valve, and several techniques have evolved to improve seat tightness. For example, the valve members are provided with a highly machined replaceable disc formed of stainless steel, or like material, which engages a highly machined contacting surface of the valve seat. Also, the valve seats are machined to relatively narrow widths which offer a small contact area with the disc member.
Another technique for achieving even greater seat tightness involves the use of a so-called "soft seat" valve configuration in which a resilient O-ring, or the like, is secured to the valve member so that contact between the outer edge of the valve seat and the O-ring provides a sealing function. However, these soft seat valves are not as durable as valves provided with the machined metal surfaces.
Still other techniques for improving seat tightness involve additional loading to the valve member utilizing external energy. However, these techniques are often complicated, not fail safe and add to the cost of the system.
Therefore, it is still a goal of designers to provide pressure relief valves with increased seal tightness, decreased fluid leakage, and increased durability without attendant increases in complexity and cost.